A loom can be provided with a system for controlling the oscillation of a yarn support roller comprising, on at least one side of the loom, a rotary cam actuating an oscillating lever connected to an arm integral with the shaft of the yarn support roller. This shaft rest, through the intermediary of raising members, in bearings supported by levers pivoted about a fixed pivot point and is connected, through the intermediary of a connecting rod, to another lever keyed on a shaft subject to the action of at least one spring. When the loom is operated continuously, this known system makes it possible to cause the axis of the yarn support roller to oscillate, in order to absorb the alternating phenomenon of excess tension or slack of the warp yarns caused by the opening or closing movement of the two sheds in the weaving process, this slack take up taking place while ensuring tensioning of the yarn by virtue of the spring.
However, at the time of re-starting the loom after a stoppage, the system in question does not make it possible to eliminate differences in the warp, i.e. differences in the number of warp threads per unit length, which create defects in the fabric, which defects are well-known to persons skilled in the art and are known as "thin spots", "marks" or "flaws". No device currently exists for preventing these defects, in high speed looms.